1. Field of the Invention
The present invention relates to an enclosure, consisting of a box or a cover for housing electronic parts or equipment to protect the electronic parts or equipment from electromagnetic interference (EMI), and to a method of manufacturing the enclosure.
2. Description of the Background Art
Electronic parts and equipment known in the art often are housed in cabinets (enclosures) made of metal which act as electromagnetic interference (EMI) shields. With the progress of technology, parts and apparatuses became more and more compact. To satisfy the demand for appropriate enclosures, plastic molded enclosures that could be efficiently produced at low costs were developed. However, such enclosures pose EMI problems.
A variety of conventional techniques are employed as the methods of EMI-shielding for plastic molded enclosures. Among these are the following: (1) a method wherein paint using a conductive material, e.g., silver or copper, as a filler, is applied to an enclosure after the molding of the enclosure, (2) a flame spraying method wherein the conductive material, e.g., silver or copper, is fused and sprayed to an enclosure by high-pressure air, (3) a vacuum metallizing method wherein metal of low boiling point (such as aluminum) is evaporated in a vacuum to form a thin film on enclosure surfaces, (4) a method wherein electroless plating of nickel, etc., is provided to an enclosure molded by high-adhesive resin, e.g., ABS resin, (5) a method wherein a molding material filled with a conductive filler, such as carbon or aluminum flakes, is used to mold an enclosure, and (6) a method wherein a composite material made by laminating a polyvinyl chloride (PVC) or polyester film to an aluminum, copper or other film is applied to an enclosure.
Also, various methods of integrally molding a metal shield material with resin have been developed.
FIG. 6(a) shows a housing for digital electronic equipment disclosed in Japanese Laid-Open Patent Publication SHO 61-22915, wherein the numeral 217' indicates resin and 215' represents a wire netting. FIG. 6(b) is a diagrammatic sectional view of dies and illustrates a molding state, wherein 211 denotes an upper die, 212 designates a lower die, 213 indicates a resin gate provided in the lower die 212, and 215 denotes an electromagnetic interference reflecting and interrupting wire netting. The wire netting 215 is placed on the lower die 212 and supplied with fused resin 217 from the gate 213, the upper die 211 is subsequently closed, and the wire netting 215 is then pressed. After cooling, the molding process is complete and the enclosure is removed. In this case, the netting must be preformed in a box shape so that corners can be properly shaped in the enclosure. The preforming of the netting into other shapes is required, depending on the final shape of the enclosure.
FIG. 7(a) shows an electronic apparatus disclosed in Japanese Laid-Open Utility Model Publication SHO 63-201391, wherein 71 indicates a metal chassis containing electronic parts, electronic circuits, etc., and 73 denotes a cover. As shown in FIG. 7(b), the metal chassis 71 houses electronic circuit cards 72. As shown in FIGS. 7(c) to 7(e), the cover 73 is made of a wire netting 74 and plastics which are formed integrally, the wire netting 74 is exposed in the periphery of the cover 73 so that when the cover 73 is fitted to the chassis 71, the wire netting 74 and chassis 71 are electrically conductive. It should be noted that a cover manufacturing method is not described in this publication.
In addition to the above, a method of inserting a preformed electromagnetic interference shield material at the time of molding is disclosed in Japanese Laid-Open Utility Model Publication SHO 59-18496 and Japanese Laid-Open Patent Publication SHO 58-115894.
The conventional methods of molding an enclosure and subsequently forming a conductive film on an enclosure surface by any of conductive paint application, conductive material flame-spraying, vacuum metallizing and resin plating are high-priced and have the problem of film peeling. Also, the method of using a molding material filled with a conductive filler to mold an enclosure does not provide a uniform dispersion of the conductive filler inside a molded product and provides a poor shielding effect.
Also, the method disclosed in Japanese Laid-Open Patent Publication SHO 61-22915 required the wire netting to be preformed, resulting in a larger number of processes and higher cost. Further, the method disclosed in Japanese Laid-Open Utility Model Publication SHO 63-201391 involves high costs because one part of the enclosure was made of metal.